Reference is made to FIG. 1-1, FIG. 1-2 and FIG. 1-3, FIG. 1-1 is a schematic view showing the structure of a wind turbine tower in the conventional technology, which shows power transmission cables inside the wind turbine tower, FIG. 1-2 is a schematic view showing the laying of the power transmission cables in FIG. 1-1, and FIG. 1-3 is a schematic view showing the structure of the power transmission cables in FIG. 1-2.
As can be seen from the above figures, lots of power transmission cables 30 are laid inside the wind turbine tower, and the power transmission cables 30 extend from a switch cabinet of a generator to pass through a base platform via the bottom of a nacelle and then enter into a reference plane at the top of the tower. A nacelle 20 and the interior thereof have a yaw movement, causing that the power transmission cables 30 also have a reciprocating twisting movement. Therefore, a saddle-shaped bracket is arranged inside the tower, and the parts, below the saddle-shaped bracket, of the cables are hanging down near the tower wall 10 in groups and are fixed, and are in a substantially vertical state as a whole.
Reference is made to FIG. 1-4 and FIG. 1-5, FIG. 1-4 is a schematic diagram of the composition of a resulting temperature outside a tower in summer in the conventional technology, and FIG. 1-5 shows resulting temperatures of the tower in the conventional technology in different orientations. FIG. 1-4 and FIG. 1-5 are each obtained by taking a practical tower within the territory of China in Northern Hemisphere as a monitoring object.
In FIG. 1-4, the resulting temperature of the tower is formed by a combined effect of solar radiation and ambient air temperature, that is, a curve 1 (indicating the resulting temperature outside the tower) is formed by superposing a curve 2 (indicating the temperature of air outside the tower) on a curve 3 (indicating an equivalent temperature of solar radiation).
In FIG. 1-5, a curve 1 indicates a resulting temperature of a horizontal direction of the tower (i.e., the temperature of the top of the tower), a curve 2 indicates a resulting temperature of an east vertical side of the tower, and a curve 3 indicates a resulting temperature of a west vertical side of the tower.
The above figures reflect:
1. The resulting temperature of the top of the nacelle is constantly higher than the resulting temperatures of the east vertical side and the west vertical side of each of the enclosures such as the tower and the nacelle 2 from 8 o'clock to 14 o'clock, and by taking 12 o'clock as a symmetry point, an exterior environment of the top of the nacelle 20 is continuously in an environment with a high resulting temperature.
2. For each of the enclosures such as the tower and the nacelle 20, the temperature at the west vertical side is higher than the temperature at the east vertical side after 8 hours.
3. After the west vertical side reaches the maximum temperature value at 16 o'clock, the temperature wave will be transferred to inner surfaces of the tower and the nacelle 20 after a delay of about half an hour; and the duration of the delay is related to a heat storage coefficient of a coating material of the tower and the nacelle and materials of the tower and the nacelle, and the magnitude of the heat storage coefficient corresponds to the duration of the delay of high temperature being transferred into the enclosure. In summer of Hami area at the southern slope of the Tianshan mountains in Sinkiang, the geographical position of Hami area determines that wind frequently blows after 18 o'clock, such that the wind power generator set keeps generating electricity at full power till dawn of the next morning. This means that the heat generated by the heat sources inside the wind power generator set continues to increase, and the falling of the external environment temperature does not immediately influence the internal environment temperature of the generator set.
In other words, the inside of the tower is always in a high temperature state, especially in summer, and in this case, the excessively high internal temperature causes the power transmission cables 30 to be difficult to dissipate heat, and the temperature of the power transmission cables 30 may even become higher, which adversely affects the service life of the power transmission cables and the safety of the entire power transmission system.